1. Field of the Invention
The present invention relates to a high frequency bar type heater inserted into a slender hole bored along a central axis of an object to be heated, for example a fastening bolt, etc., for heating the object to be heated by high frequency electromagnetic induction.
2. Description of the Prior Art
FIGS. 3(A) and 3(B) show a high frequency bar type heater in the prior art. As shown in FIG. 3(A), the high frequency bar type heater 01 in the prior art has a heat resisting and insulating tube 02 made of glass fibers or ceramics. A hairpin-shaped conductor coil 03 of one turn is inserted therein, being made of copper tubing. A magnetic core 05 of high permeability is disposed in the conductor coil 03.
The high frequency bar type heater 01 is inserted into a hole 9h of an object 9 to be heated which is of a material having an electrical conductivity, such as steel, etc. The conductor coil 03 is supplied with a large electric current of high frequency, an alternating eddy current occurs in the surrounding object 9 by electromagnetic induction, and the object 9 is exothermically heated and elevated in temperature by Joule heat of the eddy current. Cooling water for cooling the conductor coil 03 is caused to flow therewithin, so that flow of the electric current is facilitated and the generation of magnetic flux is facilitated, with the result that the electromagnetic induction is enhanced.
In the high frequency bar type heater in the prior art, as none of the heat resisting and insulating tube, the conductor coil and the magnetic core has flexibility by reasons of their material, structure, configuration, etc., the heater itself lacks flexibility as a whole. As shown in FIG. 3(B), therefore, if there is an obstruction 10 above the hole 9h of the object 9 into which the high frequency bar type heater 01 is to be inserted, a problem arises in that the high frequency bar type heater 01 cannot be inserted into the hole 9h of the object 9.